MI5 is the secret agency of which country?

MI5, officially known as the Security Service, is the United Kingdom's domestic intelligence and security agency. Its primary role is to protect national security against threats such as terrorism, espionage, cyber-attacks, and the proliferation of weapons of mass destruction. It operates within the UK, focusing on internal threats.

• The USA has intelligence agencies like the CIA (Central Intelligence Agency) for foreign intelligence and the FBI (Federal Bureau of Investigation) for domestic security.
• Russia's main intelligence agencies include the FSB (Federal Security Service) for domestic security and the SVR (Foreign Intelligence Service) for external intelligence.
• China's primary intelligence agency is the Ministry of State Security (MSS).